Mitonuclear communication in homeostasis and stress

Extending roGFP Emission via Förster-Type Resonance Energy Transfer Relay Enables Simultaneous Dual Compartment Ratiometric Redox Imaging in Live Cells

Reactive oxygen species (ROS) mediate both intercellular and intraorganellar signaling, and ROS propagate oxidative stress between cellular compartments such as mitochondria and the cytosol. Each cellular compartment contains its own sources of ROS as well as antioxidant mechanisms, which contribute to dynamic fluctuations in ROS levels that occur during signaling, metabolism, and stress. However, the coupling of redox dynamics between cellular compartments has not been well studied because of the lack of available sensors to simultaneously measure more than one subcellular compartment in the same cell. Currently, the redox-sensitive green fluorescent protein, roGFP, has been used extensively to study compartment-specific redox dynamics because it provides a quantitative ratiometric readout and it is amenable to subcellular targeting as a genetically encoded sensor. Here, we report a new family of genetically encoded fluorescent protein sensors that extend the fluorescence emission of roGFP via Förster-type resonance energy transfer to an acceptor red fluorescent protein for dual-color live-cell microscopy. We characterize the redox and optical properties of the sensor proteins, and we demonstrate that they can be used to simultaneously measure cytosolic and mitochondrial ROS in living cells. Furthermore, we use these sensors to reveal cell-to-cell heterogeneity in redox coupling between the cytosol and mitochondria when neuroblastoma cells are exposed to reductive and metabolic stresses.

Assisted reproductive technologies to prevent human mitochondrial disease transmission

Mitochondria are essential cytoplasmic organelles that generate energy (ATP) by oxidative phosphorylation and mediate key cellular processes such as apoptosis. They are maternally inherited and in humans contain a 16,569-base-pair circular genome (mtDNA) encoding 37 genes required for oxidative phosphorylation. Mutations in mtDNA cause a range of pathologies, commonly affecting energy-demanding tissues such as muscle and brain. Because mitochondrial diseases are incurable, attention has focused on limiting the inheritance of pathogenic mtDNA by mitochondrial replacement therapy (MRT). MRT aims to avoid pathogenic mtDNA transmission between generations by maternal spindle transfer, pronuclear transfer or polar body transfer: all involve the transfer of nuclear DNA from an egg or zygote containing defective mitochondria to a corresponding egg or zygote with normal mitochondria. Here we review recent developments in animal and human models of MRT and the underlying biology. These have led to potential clinical applications; we identify challenges to their technical refinement.

Targeting metabolism in cellular senescence, a role for intervention

Cellular senescence has gained much attention as a contributor to aging and susceptibility to disease. Senescent cells undergo a stable cell cycle arrest and produce pro-inflammatory cytokines. However, an additional feature of the senescence phenotype is an altered metabolic state. Despite maintaining a non-dividing state, senescent cells display a high metabolic rate. Metabolic changes characteristic of replicative senescence include altered mitochondrial function and perturbations in growth signaling pathways, such as the mTORC1-signaling pathway. Recent evidence has raised the possibility that these metabolic changes may be essential for the induction and maintenance of the senescent state. Interventions such as rapamycin treatment and methionine restriction impact key aspects of metabolism and delay cellular senescence to extend cellular lifespan. Here, we review the metabolic changes and potential metabolic regulators of the senescence program. In addition, we will discuss how lifespan-extending regimens prevent metabolic stress that accompanies and potentially regulates the senescence program.

Autophagy, its mechanisms and regulation: Implications in neurodegenerative diseases

Autophagy is a major regulatory cellular mechanism which gives the cell an ability to cope with some of the destructive events that normally occur within a metabolically living cell. This is done by maintaining the cellular homeostasis, clearance of damaged organelles and proteins and recycling necessary molecules like amino acids and fatty acids. There is a wide array of factors that influence autophagy in the state of health and disease. Disruption of these mechanisms may not only give rise to several autophagy-related disease, but also it can occur as the result of intracellular changes induced during disease pathogenesis causing exacerbation of the disease. Our knowledge is increasing regarding the role of autophagy and its mechanisms in the pathogenesis of various neurodegenerative diseases such as multiple sclerosis, Parkinson's disease, Alzheimer's disease, Huntington's disease and Amyotrophic lateral sclerosis. Indeed, getting to know about the pathways of autophagy and its regulation can provide the basis for designing therapeutic interventions. In the present paper, we review the pathways of autophagy, its regulation and the possible autophagy-targeting interventions for the treatment of neurodegenerative disorders.

Epigenetic modification of miR-663 controls mitochondria-to-nucleus retrograde signaling and tumor progression

The normal cellular function requires communication between mitochondria and the nucleus, termed mitochondria-to-nucleus retrograde signaling. Disruption of this mechanism has been implicated in the development of cancers. Many proteins are known modulators of retrograde signaling, but whether microRNAs (miRNAs) are also involved is unknown. We conducted an miRNA microarray analysis using RNA from a parental cell line, a Rho⁰ line lacking mitochondrial DNA (mtDNA) and a Rho⁰ line with restored mtDNA. We found that miR-663 was down-regulated in the mtDNA-depleted Rho⁰ line. mtDNA restoration reversed this miRNA to parental level, suggesting that miR-663 may be epigenetically regulated by retrograde signaling. By using methylation-specific PCR and bisulfite sequencing we demonstrate that miR-663 promoter is epigenetically regulated not only by genetic but also by pharmacological disruption of oxidative phosphorylation (OXPHOS). Restoration of OXPHOS Complex I inhibitor-induced miR-663 expression by N-acetylcysteine suggested that reactive oxygen species (ROS) play a key role in epigenetic regulation of miR-663. We determined that miR-663 regulates the expression of nuclear-encoded respiratory chain subunits involved in Complexes I, II, III, and IV. miR-663 also controlled the expression of the Complexes I (NDUFAF1), II (SDHAF2), III (UQCC2), and IV (SCO1) assembly factors and was required for stability of respiratory supercomplexes. Furthermore, using luciferase assays, we found that miR-663 directly regulates UQCC2. The anti-miR-663 reduced OXPHOS complex activity and increased in vitro cellular proliferation and promoted tumor development in vivo in mice. We also found that increased miR-663 expression in breast tumors consistently correlates with increased patient survival. We provide the first evidence for miRNA controlling retrograde signaling, demonstrating its epigenetic regulation and its role in breast tumorigenesis.

The integrated stress response in budding yeast lifespan extension

Aging is a complex, multi-factorial biological process shared by all living organisms. It is manifested by a gradual accumulation of molecular alterations that lead to the decline of normal physiological functions in a time-dependent fashion. The ultimate goal of aging research is to develop therapeutic means to extend human lifespan, while reducing susceptibility to many age-related diseases including cancer, as well as metabolic, cardiovascular and neurodegenerative disorders. However, this first requires elucidation of the causes of aging, which has been greatly facilitated by the use of model organisms. In particular, the budding yeast Saccharomyces cerevisiae has been invaluable in the identification of conserved molecular and cellular determinants of aging and for the development of approaches to manipulate these aging determinants to extend lifespan. Strikingly, where examined, virtually all means to experimentally extend lifespan result in the induction of cellular stress responses. This review describes growing evidence in yeast that activation of the integrated stress response contributes significantly to lifespan extension. These findings demonstrate that yeast remains a powerful model system for elucidating conserved mechanisms to achieve lifespan extension that are likely to drive therapeutic approaches to extend human lifespan and healthspan.

Protein sequestration at the nuclear periphery as a potential regulatory mechanism in premature aging

Serebryannyy and Misteli provide a perspective on how protein sequestration at the inner nuclear membrane and nuclear lamina might influence aging.

Despite the extensive description of numerous molecular changes associated with aging, insights into the driver mechanisms of this fundamental biological process are limited. Based on observations in the premature aging syndrome Hutchinson–Gilford progeria, we explore the possibility that protein regulation at the inner nuclear membrane and the nuclear lamina contributes to the aging process. In support, sequestration of nucleoplasmic proteins to the periphery impacts cell stemness, the response to cytotoxicity, proliferation, changes in chromatin state, and telomere stability. These observations point to the nuclear periphery as a central regulator of the aging phenotype.

AMPK: guardian of metabolism and mitochondrial homeostasis

Cells constantly adapt their metabolism to meet their energy needs and respond to nutrient availability. Eukaryotes have evolved a very sophisticated system to sense low cellular ATP levels via the serine/threonine kinase AMP-activated protein kinase (AMPK) complex. Under conditions of low energy, AMPK phosphorylates specific enzymes and growth control nodes to increase ATP generation and decrease ATP consumption. In the past decade, the discovery of numerous new AMPK substrates has led to a more complete understanding of the minimal number of steps required to reprogramme cellular metabolism from anabolism to catabolism. This energy switch controls cell growth and several other cellular processes, including lipid and glucose metabolism and autophagy. Recent studies have revealed that one ancestral function of AMPK is to promote mitochondrial health, and multiple newly discovered targets of AMPK are involved in various aspects of mitochondrial homeostasis, including mitophagy. This Review discusses how AMPK functions as a central mediator of the cellular response to energetic stress and mitochondrial insults and coordinates multiple features of autophagy and mitochondrial biology.

Altered bioenergetics and enhanced resistance to oxidative stress in human retinal pigment epithelial cells from donors with age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness among older adults. It has been suggested that mitochondrial defects in the retinal pigment epithelium (RPE) underlies AMD pathology. To test this idea, we developed primary cultures of RPE to ask whether RPE from donors with AMD differ in their metabolic profile compared with healthy age-matched donors. Analysis of gene expression, protein content, and RPE function showed that these cultured cells replicated many of the cardinal features of RPE in vivo. Using the Seahorse Extracellular Flux Analyzer to measure bioenergetics, we observed RPE from donors with AMD exhibited reduced mitochondrial and glycolytic function compared with healthy donors. RPE from AMD donors were also more resistant to oxidative inactivation of these two energy-producing pathways and were less susceptible to oxidation-induced cell death compared with cells from healthy donors. Investigation of the potential mechanism responsible for differences in bioenergetics and resistance to oxidative stress showed RPE from AMD donors had increased PGC1α protein as well as differential expression of multiple genes in response to an oxidative challenge. Based on our data, we propose that cultured RPE from donors phenotyped for the presence or absence of AMD provides an excellent model system for studying "AMD in a dish". Our results are consistent with the ideas that (i) a bioenergetics crisis in the RPE contributes to AMD pathology, and (ii) the diseased environment in vivo causes changes in the cellular profile that are retained in vitro.

The Reactive Species Interactome: Evolutionary Emergence, Biological Significance, and Opportunities for Redox Metabolomics and Personalized Medicine

SIGNIFICANCE

Oxidative stress is thought to account for aberrant redox homeostasis and contribute to aging and disease. However, more often than not, administration of antioxidants is ineffective, suggesting that our current understanding of the underlying regulatory processes is incomplete. Recent Advances: Similar to reactive oxygen species and reactive nitrogen species, reactive sulfur species are now emerging as important signaling molecules, targeting regulatory cysteine redox switches in proteins, affecting gene regulation, ion transport, intermediary metabolism, and mitochondrial function. To rationalize the complexity of chemical interactions of reactive species with themselves and their targets and help define their role in systemic metabolic control, we here introduce a novel integrative concept defined as the reactive species interactome (RSI). The RSI is a primeval multilevel redox regulatory system whose architecture, together with the physicochemical characteristics of its constituents, allows efficient sensing and rapid adaptation to environmental changes and various other stressors to enhance fitness and resilience at the local and whole-organism level.

CRITICAL ISSUES

To better characterize the RSI-related processes that determine fluxes through specific pathways and enable integration, it is necessary to disentangle the chemical biology and activity of reactive species (including precursors and reaction products), their targets, communication systems, and effects on cellular, organ, and whole-organism bioenergetics using system-level/network analyses.

FUTURE DIRECTIONS

Understanding the mechanisms through which the RSI operates will enable a better appreciation of the possibilities to modulate the entire biological system; moreover, unveiling molecular signatures that characterize specific environmental challenges or other forms of stress will provide new prevention/intervention opportunities for personalized medicine. Antioxid. Redox Signal. 00, 000-000.

Haploidy in Humans: An Evolutionary and Developmental Perspective

Although haploidy has not been observed in vertebrates, its natural occurrence in various eukaryotic species that had diverged from diploid ancestors suggests that there is an innate capacity for an organism to regain haploidy and that haploidy may confer evolutionary benefits. Haploid embryonic stem cells have been experimentally generated from mouse, rat, monkey, and humans. Haploidy results in major differences in cell size and gene expression levels while also affecting parental imprinting, X chromosome inactivation, and mitochondrial metabolism genes. We discuss here haploidy in evolution and the barriers to haploidy, in particular in the human context.

Repairing Mitochondrial Dysfunction in Disease

Mitochondria are essential organelles for many aspects of cellular homeostasis, including energy harvesting through oxidative phosphorylation. Alterations of mitochondrial function not only impact on cellular metabolism but also critically influence whole-body metabolism, health, and life span. Diseases defined by mitochondrial dysfunction have expanded from rare monogenic disorders in a strict sense to now also include many common polygenic diseases, including metabolic, cardiovascular, neurodegenerative, and neuromuscular diseases. This has led to an intensive search for new therapeutic and preventive strategies aimed at invigorating mitochondrial function by exploiting key components of mitochondrial biogenesis, redox metabolism, dynamics, mitophagy, and the mitochondrial unfolded protein response. As such, new findings linking mitochondrial function to the progression or outcome of this ever-increasing list of diseases has stimulated the discovery and development of the first true mitochondrial drugs, which are now entering the clinic and are discussed in this review.

Mitochondrial Nanotunnels

Insight into the regulation of complex physiological systems emerges from understanding how biological units communicate with each other. Recent findings show that mitochondria communicate at a distance with each other via nanotunnels, thin double-membrane protrusions that connect the matrices of non-adjacent mitochondria. Emerging evidence suggest that mitochondrial nanotunnels are generated by immobilized mitochondria and transport proteins. This review integrates data from the evolutionarily conserved structure and function of intercellular projections in bacteria with recent developments in mitochondrial imaging that permit nanotunnel visualization in eukaryotes. Cell type-specificity, timescales, and the selective size-based diffusion of biomolecules along nanotunnels are also discussed. The joining of individual mitochondria into dynamic networks of communicating organelles via nanotunnels and other mechanisms has major implications for organelle and cellular behaviors.

GCN5L1 modulates cross-talk between mitochondria and cell signaling to regulate FoxO1 stability and gluconeogenesis

The mitochondrial enriched GCN5-like 1 (GCN5L1) protein has been shown to modulate mitochondrial protein acetylation, mitochondrial content and mitochondrial retrograde signaling. Here we show that hepatic GCN5L1 ablation reduces fasting glucose levels and blunts hepatic gluconeogenesis without affecting systemic glucose tolerance. PEPCK and G6Pase transcript levels are downregulated in hepatocytes from GCN5L1 liver specific knockout mice and their upstream regulator, FoxO1 protein levels are decreased via proteasome-dependent degradation and via reactive oxygen species mediated ERK-1/2 phosphorylation. ERK inhibition restores FoxO1, gluconeogenic enzyme expression and glucose production. Reconstitution of mitochondrial-targeted GCN5L1 blunts mitochondrial ROS, ERK activation and increases FoxO1, gluconeogenic enzyme expression and hepatocyte glucose production. We suggest that mitochondrial GCN5L1 modulates post-translational control of FoxO1, regulates gluconeogenesis and controls metabolic pathways via mitochondrial ROS mediated ERK activation. Exploring mechanisms underpinning GCN5L1 mediated ROS signaling may expand our understanding of the role of mitochondria in gluconeogenesis control.Hepatic gluconeogenesis is tightly regulated at transcriptional level and is essential for survival during prolonged fasting. Here Wang et al. show that the mitochondrial enriched GCN5-like 1 protein controls hepatic glucose production by regulating FoxO1 protein levels via proteasome-dependent degradation and, in turn, gluconeogenic gene expression.

Role of mitochondrial dysfunction and dysregulation of Ca2+ homeostasis in the pathophysiology of insulin resistance and type 2 diabetes

Metabolic diseases such as obesity, type 2 diabetes (T2D) and insulin resistance have attracted great attention from biomedical researchers and clinicians because of the astonishing increase in its prevalence. Decrease in the capacity of oxidative metabolism and mitochondrial dysfunction are a major contributor to the development of these metabolic disorders. Recent studies indicate that alteration of intracellular Ca²⁺ levels and downstream Ca²⁺-dependent signaling pathways appear to modulate gene transcription and the activities of many enzymes involved in cellular metabolism. Ca²⁺ uptake into mitochondria modulates a number of Ca²⁺-dependent proteins and enzymes participating in fatty acids metabolism, tricarboxylic acid cycle, oxidative phosphorylation and apoptosis in response to physiological and pathophysiological conditions. Mitochondrial calcium uniporter (MCU) complex has been identified as a major channel located on the inner membrane to regulate Ca²⁺ transport into mitochondria. Recent studies of MCU complex have increased our understanding of the modulation of mitochondrial function and retrograde signaling to the nucleus via regulation of the mitochondrial Ca²⁺ level. Mitochondria couple cellular metabolic state by regulating not only their own Ca²⁺ levels, but also influence the entire network of cellular Ca²⁺ signaling. The mitochondria-associated ER membranes (MAMs), which are specialized structures between ER and mitochondria, are responsible for efficient communication between these organelles. Defects in the function or structure of MAMs have been observed in affected tissue cells in metabolic disease or neurodegenerative disorders. We demonstrated that dysregulation of intracellular Ca²⁺ homeostasis due to mitochondrial dysfunction or defects in the function of MAMs are involved in the pathogenesis of insulin insensitivity and T2D. These observations suggest that mitochondrial dysfunction and disturbance of Ca²⁺ homeostasis warrant further studies to assist the development of therapeutics for prevention and medication of insulin resistance and T2D.

MCbiclust: a novel algorithm to discover large-scale functionally related gene sets from massive transcriptomics data collections

The potential to understand fundamental biological processes from gene expression data has grown in parallel with the recent explosion of the size of data collections. However, to exploit this potential, novel analytical methods are required, capable of discovering large co-regulated gene networks. We found current methods limited in the size of correlated gene sets they could discover within biologically heterogeneous data collections, hampering the identification of multi-gene controlled fundamental cellular processes such as energy metabolism, organelle biogenesis and stress responses. Here we describe a novel biclustering algorithm called Massively Correlated Biclustering (MCbiclust) that selects samples and genes from large datasets with maximal correlated gene expression, allowing regulation of complex networks to be examined. The method has been evaluated using synthetic data and applied to large bacterial and cancer cell datasets. We show that the large biclusters discovered, so far elusive to identification by existing techniques, are biologically relevant and thus MCbiclust has great potential in the analysis of transcriptomics data to identify large-scale unknown effects hidden within the data. The identified massive biclusters can be used to develop improved transcriptomics based diagnosis tools for diseases caused by altered gene expression, or used for further network analysis to understand genotype-phenotype correlations.

Mitochondrial-epigenetic crosstalk in environmental toxicology

Crosstalk between the nuclear epigenome and mitochondria, both in normal physiological function and in responses to environmental toxicant exposures, is a developing sub-field of interest in environmental and molecular toxicology. The majority (∼99%) of mitochondrial proteins are encoded in the nuclear genome, so programmed communication among nuclear, cytoplasmic, and mitochondrial compartments is essential for maintaining cellular health. In this review, we will focus on correlative and mechanistic evidence for direct impacts of each system on the other, discuss demonstrated or potential crosstalk in the context of chemical insult, and highlight biological research questions for future study. We will first review the two main signaling systems: nuclear signaling to the mitochondria [anterograde signaling], best described in regulation of oxidative phosphorylation (OXPHOS) and mitochondrial biogenesis in response to environmental signals received by the nucleus, and mitochondrial signals to the nucleus [retrograde signaling]. Both signaling systems can communicate intracellular energy needs or a need to compensate for dysfunction to maintain homeostasis, but both can also relay inappropriate signals in the presence of dysfunction in either system and contribute to adverse health outcomes. We will first review these two signaling systems and highlight known or biologically feasible epigenetic contributions to both, then briefly discuss the emerging field of epigenetic regulation of the mitochondrial genome, and finally discuss putative "crosstalk phenotypes", including biological phenomena, such as caloric restriction, maintenance of stemness, and circadian rhythm, and states of disease or loss of function, such as cancer and aging, in which both the nuclear epigenome and mitochondria are strongly implicated.

Genomic and functional integrity of the hematopoietic system requires tolerance of oxidative DNA lesions

Endogenous DNA damage is causally associated with the functional decline and transformation of stem cells that characterize aging. DNA lesions that have escaped DNA repair can induce replication stress and genomic breaks that induce senescence and apoptosis. It is not clear how stem and proliferating cells cope with accumulating endogenous DNA lesions and how these ultimately affect the physiology of cells and tissues. Here we have addressed these questions by investigating the hematopoietic system of mice deficient for Rev1, a core factor in DNA translesion synthesis (TLS), the postreplicative bypass of damaged nucleotides. Rev1 hematopoietic stem and progenitor cells displayed compromised proliferation, and replication stress that could be rescued with an antioxidant. The additional disruption of Xpc, essential for global-genome nucleotide excision repair (ggNER) of helix-distorting nucleotide lesions, resulted in the perinatal loss of hematopoietic stem cells, progressive loss of bone marrow, and fatal aplastic anemia between 3 and 4 months of age. This was associated with replication stress, genomic breaks, DNA damage signaling, senescence, and apoptosis in bone marrow. Surprisingly, the collapse of the Rev1Xpc bone marrow was associated with progressive mitochondrial dysfunction and consequent exacerbation of oxidative stress. These data reveal that, to protect its genomic and functional integrity, the hematopoietic system critically depends on the combined activities of repair and replication of helix-distorting oxidative nucleotide lesions by ggNER and Rev1-dependent TLS, respectively. The error-prone nature of TLS may provide mechanistic understanding of the accumulation of mutations in the hematopoietic system upon aging.

Regulation of longevity by FGF21: Interaction between energy metabolism and stress responses

Fibroblast growth factor 21 (FGF21) is a hormone-like member of FGF family which controls metabolic multiorgan crosstalk enhancing energy expenditure through glucose and lipid metabolism. In addition, FGF21 acts as a stress hormone induced by endoplasmic reticulum stress and dysfunctions of mitochondria and autophagy in several tissues. FGF21 also controls stress responses and metabolism by modulating the functions of somatotropic axis and hypothalamic-pituitary-adrenal (HPA) pathway. FGF21 is a potent longevity factor coordinating interactions between energy metabolism and stress responses. Recent studies have revealed that FGF21 treatment can alleviate many age-related metabolic disorders, e.g. atherosclerosis, obesity, type 2 diabetes, and some cardiovascular diseases. In addition, transgenic mice overexpressing FGF21 have an extended lifespan. However, chronic metabolic and stress-related disorders involving inflammatory responses can provoke FGF21 resistance and thus disturb healthy aging process. First, we will describe the role of FGF21 in interorgan energy metabolism and explain how its functions as a stress hormone can improve healthspan. Next, we will examine both the induction of FGF21 expression via the integrated stress response and the molecular mechanism through which FGF21 enhances healthy aging. Finally, we postulate that FGF21 resistance, similarly to insulin resistance, jeopardizes human healthspan and accelerates the aging process.

microRNA-mediated differential expression of TRMU, GTPBP3 and MTO1 in cell models of mitochondrial-DNA diseases

Mitochondrial diseases due to mutations in the mitochondrial (mt) DNA are heterogeneous in clinical manifestations but usually include OXPHOS dysfunction. Mechanisms by which OXPHOS dysfunction contributes to the disease phenotype invoke, apart from cell energy deficit, maladaptive responses to mitochondria-to-nucleus retrograde signaling. Here we used five different cybrid models of mtDNA diseases to demonstrate that the expression of the nuclear-encoded mt-tRNA modification enzymes TRMU, GTPBP3 and MTO1 varies in response to specific pathological mtDNA mutations, thus altering the modification status of mt-tRNAs. Importantly, we demonstrated that the expression of TRMU, GTPBP3 and MTO1 is regulated by different miRNAs, which are induced by retrograde signals like ROS and Ca²⁺ via different pathways. Our data suggest that the up- or down-regulation of the mt-tRNA modification enzymes is part of a cellular response to cope with a stoichiometric imbalance between mtDNA- and nuclear-encoded OXPHOS subunits. However, this miRNA-mediated response fails to provide full protection from the OXPHOS dysfunction; rather, it appears to aggravate the phenotype since transfection of the mutant cybrids with miRNA antagonists improves the energetic state of the cells, which opens up options for new therapeutic approaches.

Mitochondrially derived peptides as novel regulators of metabolism

Mitochondrially derived peptides represent a new class of circulating signalling molecules. Humanin, the first member of this class, has been shown to have several metabolic effects such as reducing weight gain and visceral fat and increasing glucose-stimulated insulin release. The discovery of several other new members, such as MOTS-c and SHLP1-6, has further added to this group. These new peptides have also been found to affect metabolism with MOTS-c potently decreasing weight gain in mice on a high-fat diet. This review covers the basic biology of this class of peptides and discusses the relevance to organismal metabolism.

Multi-omics analysis identifies ATF4 as a key regulator of the mitochondrial stress response in mammals

Mitochondrial stress activates a mitonuclear response to safeguard and repair mitochondrial function and to adapt cellular metabolism to stress. Using a multiomics approach in mammalian cells treated with four types of mitochondrial stressors, we identify activating transcription factor 4 (ATF4) as the main regulator of the stress response. Surprisingly, canonical mitochondrial unfolded protein response genes mediated by ATF5 are not activated. Instead, ATF4 activates the expression of cytoprotective genes, which reprogram cellular metabolism through activation of the integrated stress response (ISR). Mitochondrial stress promotes a local proteostatic response by reducing mitochondrial ribosomal proteins, inhibiting mitochondrial translation, and coupling the activation of the ISR with the attenuation of mitochondrial function. Through a trans-expression quantitative trait locus analysis, we provide genetic evidence supporting a role for Fh1 in the control of Atf4 expression in mammals. Using gene expression data from mice and humans with mitochondrial diseases, we show that the ATF4 pathway is activated in vivo upon mitochondrial stress. Our data illustrate the value of a multiomics approach to characterize complex cellular networks and provide a versatile resource to identify new regulators of mitochondrial-related diseases.

ATF4 helps mitochondria pass the stress test

The transcription factor ATF4 coordinates the mitochondrial stress response in mammalian cells.

A systems pharmacology-based approach to identify novel Kv1.3 channel-dependent mechanisms in microglial activation

BACKGROUND

Kv1.3 potassium channels regulate microglial functions and are overexpressed in neuroinflammatory diseases. Kv1.3 blockade may selectively inhibit pro-inflammatory microglia in neurological diseases but the molecular and cellular mechanisms regulated by Kv1.3 channels are poorly defined.

METHODS

We performed immunoblotting and flow cytometry to confirm Kv1.3 channel upregulation in lipopolysaccharide (LPS)-activated BV2 microglia and in brain mononuclear phagocytes freshly isolated from LPS-treated mice. Quantitative proteomics was performed on BV2 microglia treated with control, LPS, ShK-223 (highly selective Kv1.3 blocker), and LPS+ShK-223. Gene ontology (GO) analyses of Kv1.3-dependent LPS-regulated proteins were performed, and the most representative proteins and GO terms were validated. Effects of Kv1.3-blockade on LPS-activated BV2 microglia were studied in migration, focal adhesion formation, reactive oxygen species production, and phagocytosis assays. In vivo validation of protein changes and predicted molecular pathways were performed in a model of systemic LPS-induced neuroinflammation, employing antigen presentation and T cell proliferation assays. Informed by pathway analyses of proteomic data, additional mechanistic experiments were performed to identify early Kv1.3-dependent signaling and transcriptional events.

RESULTS

LPS-upregulated cell surface Kv1.3 channels in BV2 microglia and in microglia and CNS-infiltrating macrophages isolated from LPS-treated mice. Of 144 proteins differentially regulated by LPS (of 3141 proteins), 21 proteins showed rectification by ShK-223. Enriched cellular processes included MHCI-mediated antigen presentation (TAP1, EHD1), cell motility, and focal adhesion formation. In vitro, ShK-223 decreased LPS-induced focal adhesion formation, reversed LPS-induced inhibition of migration, and inhibited LPS-induced upregulation of EHD1, a protein involved in MHCI trafficking. In vivo, intra-peritoneal ShK-223 inhibited LPS-induced MHCI expression by CD11b⁺CD45^low microglia without affecting MHCI expression or trafficking of CD11b⁺CD45^high macrophages. ShK-223 inhibited LPS-induced MHCI-restricted antigen presentation to ovalbumin-specific CD8⁺ T cells both in vitro and in vivo. Kv1.3 co-localized with the LPS receptor complex and regulated LPS-induced early serine (S727) STAT1 phosphorylation.

CONCLUSIONS

We have unraveled novel molecular and functional roles for Kv1.3 channels in pro-inflammatory microglial activation, including a Kv1.3 channel-regulated pathway that facilitates MHCI expression and MHCI-dependent antigen presentation by microglia to CD8⁺ T cells. We also provide evidence for neuro-immunomodulation by systemically administered ShK peptides. Our results further strengthen the therapeutic candidacy of microglial Kv1.3 channels in neurologic diseases.

A role for TSPO in mitochondrial Ca2+ homeostasis and redox stress signaling

The 18 kDa translocator protein TSPO localizes on the outer mitochondrial membrane (OMM). Systematically overexpressed at sites of neuroinflammation it is adopted as a biomarker of brain conditions. TSPO inhibits the autophagic removal of mitochondria by limiting PARK2-mediated mitochondrial ubiquitination via a peri-organelle accumulation of reactive oxygen species (ROS). Here we describe that TSPO deregulates mitochondrial Ca2+ signaling leading to a parallel increase in the cytosolic Ca2+ pools that activate the Ca2+-dependent NADPH oxidase (NOX) thereby increasing ROS. The inhibition of mitochondrial Ca2+ uptake by TSPO is a consequence of the phosphorylation of the voltage-dependent anion channel (VDAC1) by the protein kinase A (PKA), which is recruited to the mitochondria, in complex with the Acyl-CoA binding domain containing 3 (ACBD3). Notably, the neurotransmitter glutamate, which contributes neuronal toxicity in age-dependent conditions, triggers this TSPO-dependent mechanism of cell signaling leading to cellular demise. TSPO is therefore proposed as a novel OMM-based pathway to control intracellular Ca2+ dynamics and redox transients in neuronal cytotoxicity.

Mitochondrial form, function and signalling in aging

Aging is often accompanied by a decline in mitochondrial mass and function in different tissues. Additionally, cell resistance to stress is frequently found to be prevented by higher mitochondrial respiratory capacity. These correlations strongly suggest mitochondria are key players in aging and senescence, acting by regulating energy homeostasis, redox balance and signalling pathways central in these processes. However, mitochondria display a wide array of functions and signalling properties, and the roles of these different characteristics are still widely unexplored. Furthermore, differences in mitochondrial properties and responses between tissues and cell types, and how these affect whole body metabolism are also still poorly understood. This review uncovers aspects of mitochondrial biology that have an impact upon aging in model organisms and selected mammalian cells and tissues.

DNA damage related crosstalk between the nucleus and mitochondria

The electron transport chain is the primary pathway by which a cell generates energy in the form of ATP. Byproducts of this process produce reactive oxygen species that can cause damage to mitochondrial DNA. If not properly repaired, the accumulation of DNA damage can lead to mitochondrial dysfunction linked to several human disorders including neurodegenerative diseases and cancer. Mitochondria are able to combat oxidative DNA damage via repair mechanisms that are analogous to those found in the nucleus. Of the repair pathways currently reported in the mitochondria, the base excision repair pathway is the most comprehensively described. Proteins that are involved with the maintenance of mtDNA are encoded by nuclear genes and translocate to the mitochondria making signaling between the nucleus and mitochondria imperative. In this review, we discuss the current understanding of mitochondrial DNA repair mechanisms and also highlight the sensors and signaling pathways that mediate crosstalk between the nucleus and mitochondria in the event of mitochondrial stress.

Linezolid-induced lactic acidosis: the thin line between bacterial and mitochondrial ribosomes

INTRODUCTION

Linezolid inhibits bacterial growth by targeting bacterial ribosomes and by interfering with bacterial protein synthesis. Lactic acidosis is a rare, but potentially lethal, side effect of linezolid. Areas covered: The pathogenesis of linezolid-induced lactic acidosis is reviewed with special emphasis on aspects relevant to the recognition, prevention and treatment of the syndrome. Expert opinion: Linezolid-induced lactic acidosis reflects the untoward interaction between the drug and mitochondrial ribosomes. The inhibition of mitochondrial protein synthesis diminishes the respiratory chain enzyme content and thus limits aerobic energy production. As a result, anaerobic glycolysis and lactate generation accelerate independently from tissue hypoxia. In the absence of any confirmatory test, linezolid-induced lactic acidosis should be suspected only after exclusion of other, more common, causes of lactic acidosis such as hypoxemia, anemia or low cardiac output. Normal-to-high whole-body oxygen delivery, high venous oxygen saturation and lack of response to interventions that effectively increase tissue oxygen provision all suggest a primary defect in oxygen use at the mitochondrial level. During prolonged therapy with linezolid, blood drug and lactate levels should be regularly monitored. The current standard-of-care treatment of linezolid-induced lactic acidosis consists of drug withdrawal to reverse mitochondrial intoxication and intercurrent life support.

Regulation of the H+-ATP synthase by IF1: a role in mitohormesis

The mitochondrial H+-ATP synthase is a primary hub of cellular homeostasis by providing the energy required to sustain cellular activity and regulating the production of signaling molecules that reprogram nuclear activity needed for adaption to changing cues. Herein, we summarize findings regarding the regulation of the activity of the H+-ATP synthase by its physiological inhibitor, the ATPase inhibitory factor 1 (IF1) and their functional role in cellular homeostasis. First, we outline the structure and the main molecular mechanisms that regulate the activity of the enzyme. Next, we describe the molecular biology of IF1 and summarize the regulation of IF1 expression and activity as an inhibitor of the H+-ATP synthase emphasizing the role of IF1 as a main driver of energy rewiring and cellular signaling in cancer. Findings in transgenic mice in vivo indicate that the overexpression of IF1 is sufficient to reprogram energy metabolism to an enhanced glycolysis and activate reactive oxygen species (ROS)-dependent signaling pathways that promote cell survival. These findings are placed in the context of mitohormesis, a program in which a mild mitochondrial stress triggers adaptive cytoprotective mechanisms that improve lifespan. In this regard, we emphasize the role played by the H+-ATP synthase in modulating signaling pathways that activate the mitohormetic response, namely ATP, ROS and target of rapamycin (TOR). Overall, we aim to highlight the relevant role of the H+-ATP synthase and of IF1 in cellular physiology and the need of additional studies to decipher their contributions to aging and age-related diseases.

Mitophagy Transcriptome: Mechanistic Insights into Polyphenol-Mediated Mitophagy

Mitochondria are important bioenergetic and signalling hubs critical for myriad cellular functions and homeostasis. Dysfunction in mitochondria is a central theme in aging and diseases. Mitophagy, a process whereby damaged mitochondria are selectively removed by autophagy, plays a key homeostatic role in mitochondrial quality control. Upregulation of mitophagy has shown to mitigate superfluous mitochondrial accumulation and toxicity to safeguard mitochondrial fitness. Hence, mitophagy is a viable target to promote longevity and prevent age-related pathologies. Current challenge in modulating mitophagy for cellular protection involves identification of physiological ways to activate the pathway. Till date, mitochondrial stress and toxins remain the most potent inducers of mitophagy. Polyphenols have recently been demonstrated to protect mitochondrial health by facilitating mitophagy, thus suggesting the exciting prospect of augmenting mitophagy through dietary intake. In this review, we will first discuss the different surveillance mechanisms responsible for the removal of damaged mitochondrial components, followed by highlighting the transcriptional regulatory mechanisms of mitophagy. Finally, we will review the functional connection between polyphenols and mitophagy and provide insight into the underlying mechanisms that potentially govern polyphenol-induced mitophagy.

Convergence of mitochondrial and chloroplastic ANAC017/PAP-dependent retrograde signalling pathways and suppression of programmed cell death

The energy-converting organelles mitochondria and chloroplasts are tightly embedded in cellular metabolism and stress response. To appropriately control organelle function, extensive regulatory mechanisms are at play that involve two-way exchange between the nucleus and mitochondria/chloroplasts. In recent years, our understanding of how mitochondria and chloroplasts provide 'retrograde' feedback to the nucleus, resulting in targeted transcriptional changes, has greatly increased. Nevertheless, mitochondrial and chloroplast retrograde signalling have largely been studied independently, and only few points of interaction have been found or proposed. Through reassessment of recent publications, this perspective proposes that two of the most well-studied retrograde signalling pathways in plants, those mediated by ANAC017 and those mediated by phosphoadenosine phosphate (PAP), are most likely convergent and can direct overlapping genes. Furthermore, at least part of this common retrograde response appears targeted towards suppression of programmed cell death (PCD) triggered by organellar defects. The identified target genes are discussed in light of their roles in PCD suppression and amplifying the signalling cascade via positive-feedback loops. Finally, a mechanism is proposed that may explain why the convergence of PAP/ANAC017-dependent signalling appears capable of suppressing some types of PCD lesions, but not others, based on the subcellular location of the initial PCD-inducing dysfunction.

ONC201 Demonstrates Antitumor Effects in Both Triple-Negative and Non-Triple-Negative Breast Cancers through TRAIL-Dependent and TRAIL-Independent Mechanisms

Breast cancer is a major cause of cancer-related death. TNF-related apoptosis-inducing ligand (TRAIL) has been of interest as a cancer therapeutic, but only a subset of triple-negative breast cancers (TNBC) is sensitive to TRAIL. The small-molecule ONC201 induces expression of TRAIL and its receptor DR5. ONC201 has entered clinical trials in advanced cancers. Here, we show that ONC201 is efficacious against both TNBC and non-TNBC cells (n = 13). A subset of TNBC and non-TNBC cells succumbs to ONC201-induced cell death. In 2 of 8 TNBC cell lines, ONC201 treatment induces caspase-8 cleavage and cell death that is blocked by TRAIL-neutralizing antibody RIK2. The proapoptotic effect of ONC201 translates to in vivo efficacy in the MDA-MB-468 xenograft model. In most TNBC lines tested (6/8), ONC201 has an antiproliferative effect but does not induce apoptosis. ONC201 decreases cyclin D1 expression and causes an accumulation of cells in the G₁ phase of the cell cycle. pRb expression is associated with sensitivity to the antiproliferative effects of ONC201, and the compound synergizes with taxanes in less sensitive cells. All non-TNBC cells (n = 5) are growth inhibited following ONC201 treatment, and unlike what has been observed with TRAIL, a subset (n = 2) shows PARP cleavage. In these cells, cell death induced by ONC201 is TRAIL independent. Our data demonstrate that ONC201 has potent antiproliferative and proapoptotic effects in a broad range of breast cancer subtypes, through TRAIL-dependent and TRAIL-independent mechanisms. These findings develop a preclinical rationale for developing ONC201 as a single agent and/or in combination with approved therapies in breast cancer. Mol Cancer Ther; 16(7); 1290-8. ©2017 AACR.

Mutant eIF2B leads to impaired mitochondrial oxidative phosphorylation in vanishing white matter disease

Eukaryotic translation initiation factor 2B (eIF2B) is a master regulator of protein synthesis under normal and stress conditions. Mutations in any of the five genes encoding its subunits lead to vanishing white matter (VWM) disease, a recessive genetic deadly illness caused by progressive loss of white matter in the brain. In this study we used fibroblasts, which are not involved in the disease, to demonstrate the involvement of eIF2B in mitochondrial function and abundance. Mass spectrometry of total proteome of mouse embryonic fibroblasts (MEFs) isolated from Eif2b5^R132H/R132H mice revealed unbalanced stoichiometry of proteins involved in oxidative phosphorylation and of mitochondrial translation machinery components, among others. Mutant MEFs exhibit 55% decrease in oxygen consumption rate per mtDNA content and 47% increase in mitochondrial abundance (p < 0.005), reflecting adaptation to energy requirements. A more robust eIF2B-associated oxidative respiration deficiency was found in mutant primary astrocytes, which exhibit > 3-fold lower ATP-linked respiration per cell despite a 2-fold increase in mtDNA content (p < 0.03). The 2-fold increase in basal and stimulated glycolysis in mutant astrocytes (p ≤ 0.03), but not in MEFs, demonstrates their higher energetic needs and further explicates their involvement in the disease. The data demonstrate the critical role of eIF2B in tight coordination of expression from nuclear and mitochondrial genomes and illuminates the importance of mitochondrial function in VWM pathology. Further dissection of the signaling network associated with eIF2B function will help generating therapeutic strategies for VWM disease and possibly other neurodegenerative disorders.

Stress-induced dynamic regulation of mitochondrial STAT3 and its association with cyclophilin D reduce mitochondrial ROS production

Signal transducer and activator of transcription 3 (STAT3) is associated with various physiological and pathological functions, mainly as a transcription factor that translocates to the nucleus upon tyrosine phosphorylation induced by cytokine stimulation. In addition, a small pool of STAT3 resides in the mitochondria, where it serves as a sensor for various metabolic stressors including reactive oxygen species (ROS). Mitochondrially localized STAT3 largely exerts its effects through direct or indirect regulation of the activity of the electron transport chain (ETC). It has been assumed that the amounts of STAT3 in the mitochondria are static. We showed that various stimuli, including oxidative stress and cytokines, triggered a signaling cascade that resulted in a rapid loss of mitochondrially localized STAT3. Recovery of the mitochondrial pool of STAT3 over time depended on phosphorylation of Ser727 in STAT3 and new protein synthesis. Under these conditions, mitochondrially localized STAT3 also became competent to bind to cyclophilin D (CypD). Binding of STAT3 to CypD was mediated by the amino terminus of STAT3, which was also important for reducing mitochondrial ROS production after oxidative stress. These results outline a role for mitochondrially localized STAT3 in sensing and responding to external stimuli.

Clearing the outer mitochondrial membrane from harmful proteins via lipid droplets

In recent years it turned out that there is not only extensive communication between the nucleus and mitochondria but also between mitochondria and lipid droplets (LDs) as well. We were able to demonstrate that a number of proteins shuttle between LDs and mitochondria and it depends on the metabolic state of the cell on which organelle these proteins are predominantly localized. Responsible for the localization of the particular proteins is a protein domain consisting of two α-helices, which we termed V-domain according to the predicted structure. So far we have detected this domain in the following proteins: mammalian BAX, BCL-XL, TCTP and yeast Mmi1p and Erg6p. According to our experiments there are two functions of this domain: (1) shuttling of proteins to mitochondria in times of stress and apoptosis; (2) clearing the outer mitochondrial membrane from pro- as well as anti-apoptotic proteins by moving them to LDs after the stress ceases. In this way the LDs are used by the cell to modulate stress response.

ABCB10 depletion reduces unfolded protein response in mitochondria

Mitochondria have many functions, including ATP generation. The electron transport chain (ETC) and the coupled ATP synthase generate ATP by consuming oxygen. Reactive oxygen species (ROS) are also produced by ETC, and ROS damage deoxyribonucleic acids, membrane lipids and proteins. Recent analysis indicate that mitochondrial unfolded protein response (UPR^mt), which enhances expression of mitochondrial chaperones and proteases to remove damaged proteins, is activated when damaged proteins accumulate in the mitochondria. In Caenorhabditis elegans, HAF-1, a putative ortholog of human ABCB10, plays an essential role in signal transduction from mitochondria to nuclei to enhance UPR^mt. Therefore, it is possible that ABCB10 has a role similar to that of HAF-1. However, it has not been reported whether ABCB10 is a factor in the signal transduction pathway to enhance UPR^mt. In this study, ABCB10 was depleted in HepG2 cells using small interfering RNA (siRNA), and the effect was examined. ABCB10 depletion upregulated ROS and the expression of ROS-detoxifying enzymes (SOD2, GSTA1, and GSTA2), and SESN3, a protein induced by ROS to protect the cell from oxidative stress. In addition, ABCB10 depletion significantly decreased expression of UPR^mt-related mitochondrial chaperones (HSPD1 and DNAJA3), and a mitochondrial protease (LONP1). However, the putative activity of ABCB10 to export peptides from mitochondria was not lost by ABCB10 depletion. Altogether, these data suggest that ABCB10 is involved in UPR^mt signaling pathway similar to that of HAF-1, although ABCB10 probably does not participate in peptide export from mitochondria.

Mitochondria and Epigenetics - Crosstalk in Homeostasis and Stress

Through epigenetic mechanisms cells integrate environmental stimuli to fine-tune gene expression levels. Mitochondrial function is essential to provide the intermediate metabolites necessary to generate and modify epigenetic marks in the nucleus, which in turn can regulate the expression of mitochondrial proteins. In this review we summarize the function of mitochondria in the regulation of epigenetic mechanisms as a new aspect of mitonuclear communication. We focus in particular on the most common epigenetic modifications - histone acetylation and histone and DNA methylation. We also discuss the emerging field of mitochondrial DNA (mtDNA) methylation, whose physiological role remains unknown. Finally, we describe the essential role of some histone modifications in regulating the mitochondrial unfolded protein response (UPR^mt) and the mitochondrial stress-dependent lifespan extension.

Asymmetric Arginine Dimethylation Modulates Mitochondrial Energy Metabolism and Homeostasis in Caenorhabditis elegans

Protein arginine methyltransferase 1 (PRMT-1) catalyzes asymmetric arginine dimethylation on cellular proteins and modulates various aspects of biological processes, such as signal transduction, DNA repair, and transcriptional regulation. We have previously reported that the null mutant of prmt-1 in Caenorhabditis elegans exhibits a slightly shortened life span, but the physiological significance of PRMT-1 remains largely unclear. Here we explored the role of PRMT-1 in mitochondrial function as hinted by a two-dimensional Western blot-based proteomic study. Subcellular fractionation followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis showed that PRMT-1 is almost entirely responsible for asymmetric arginine dimethylation on mitochondrial proteins. Importantly, isolated mitochondria from prmt-1 mutants represent compromised ATP synthesis in vitro, and whole-worm respiration in prmt-1 mutants is decreased in vivo Transgenic rescue experiments demonstrate that PRMT-1-dependent asymmetric arginine dimethylation is required to prevent mitochondrial reactive oxygen species (ROS) production, which consequently causes the activation of the mitochondrial unfolded-protein response. Furthermore, the loss of enzymatic activity of prmt-1 induces food avoidance behavior due to mitochondrial dysfunction, but treatment with the antioxidant N-acetylcysteine significantly ameliorates this phenotype. These findings add a new layer of complexity to the posttranslational regulation of mitochondrial function and provide clues for understanding the physiological roles of PRMT-1 in multicellular organisms.

Vitamin B3 modulates mitochondrial vulnerability and prevents glaucoma in aged mice

Glaucomas are neurodegenerative diseases that cause vision loss, especially in the elderly. The mechanisms initiating glaucoma and driving neuronal vulnerability during normal aging are unknown. Studying glaucoma-prone mice, we show that mitochondrial abnormalities are an early driver of neuronal dysfunction, occurring before detectable degeneration. Retinal levels of nicotinamide adenine dinucleotide (NAD+, a key molecule in energy and redox metabolism) decrease with age and render aging neurons vulnerable to disease-related insults. Oral administration of the NAD+ precursor nicotinamide (vitamin B3), and/or gene therapy (driving expression of Nmnat1, a key NAD+-producing enzyme), was protective both prophylactically and as an intervention. At the highest dose tested, 93% of eyes did not develop glaucoma. This supports therapeutic use of vitamin B3 in glaucoma and potentially other age-related neurodegenerations.

Nutrients in Energy and One-Carbon Metabolism: Learning from Metformin Users

Metabolic vulnerability is associated with age-related diseases and concomitant co-morbidities, which include obesity, diabetes, atherosclerosis and cancer. Most of the health problems we face today come from excessive intake of nutrients and drugs mimicking dietary effects and dietary restriction are the most successful manipulations targeting age-related pathways. Phenotypic heterogeneity and individual response to metabolic stressors are closely related food intake. Understanding the complexity of the relationship between dietary provision and metabolic consequences in the long term might provide clinical strategies to improve healthspan. New aspects of metformin activity provide a link to many of the overlapping factors, especially the way in which organismal bioenergetics remodel one-carbon metabolism. Metformin not only inhibits mitochondrial complex 1, modulating the metabolic response to nutrient intake, but also alters one-carbon metabolic pathways. Here, we discuss findings on the mechanism(s) of action of metformin with the potential for therapeutic interpretations.

Mitochondria Damage and Kidney Disease

The kidney is a vital organ that demands an extraordinary amount of energy to actively maintain the body's metabolism, plasma hemodynamics, electrolytes and water homeostasis, nutrients reabsorption, and hormone secretion. Kidney is only second to the heart in mitochondrial count and oxygen consumption. As such, the health and status of the energy power house, the mitochondria, is pivotal to the health and proper function of the kidney. Mitochondria are heterogeneous and highly dynamic organelles and their functions are subject to complex regulations through modulation of its biogenesis, bioenergetics, dynamics and clearance within cell. Kidney diseases, either acute kidney injury (AKI) or chronic kidney disease (CKD), are important clinical issues and global public health concerns with high mortality rate and socioeconomic burden due to lack of effective therapeutic strategies to cure or retard the progression of the diseases. Mitochondria-targeted therapeutics has become a major focus for modern research with the belief that maintaining mitochondria homeostasis can prevent kidney pathogenesis and disease progression. A better understanding of the cellular and molecular events that govern mitochondria functions in health and disease will potentially lead to improved therapeutics development.